This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Lanthanum carbonate (LaCO3) is an oral phosphate binder widely used in end-stage renal disease (ESRD). Preclinical animal studies reported the highest La concentrations outside the gut to be in mesenteric lymph nodes. We observed previously unreported La deposition visible by light microscopy and confirmed by scanning electron microscopy with energy dispersive x-ray spectroscopy in a mesenteric lymph node at autopsy of a 38-year-old female ESRD patient 3 years following LaCO3 administration. Although LaCO3 is generally thought to be minimally absorbed, this demonstration suggests the need for further investigation of the extent and potential effects of such absorption. To this end samples will be measured using the microprobe at BL 2-3 at SSRL to examine the extent of La and Ga distribution and the chemical forms of the deposits.